Process for the preparation of polyhydroxydibasic acids and their salts



"Patented Jan. 4,

. 2,338,114 I raocass roa m PREPARATION or Pony-p a main mm SALTS oxrnmssro ACIDS AND Thevinvention described hereinmay be manuiactured and used by or for the Government for governmental purposes without the payment to .meoi anyroyalty thereon. 1 The, present invention relates-to a process of preparing polyhydroxydibasic acids and their Itisan biect of the presentinventionto provide an improved processior the conversion of uronic acids ortheir salts to salts of dibasic acids, and the recovery of the acids from the reaction mixture. Other objects 01' the invention will appear more fully from the following specificaq tion.

Uronic acids occur in large quantities in many.

natural products, as, for example, in the pectins, gums. and various polysaccharides. These abundant raw materials provide cheap, starting substances iorthepreparation oi dibasic salts and their acids by the present invention.

In accordance with the present invention, the

' conversion of the vuronic acids or their salts to salts of polyhydroxydlcarboxylic acids containing one carbon less than the 'parent acid, is'

effected by the treatment thereof with oxygen while in alkaline solution.

The practice of the present invention is illustrated by the following examples in which ordinary laboratory equipment may be used.

Example 1 Approximately 100 grams of a uronic'acid, such 7 as galacturonic' acid, is dissolvedin 2.5 liters of normal potassium hydroxide solution which prei erably has been previously saturated with oxygen.

Oxygen is then introduced into the solution which I is agitated by means 0! a conventional stirrer,

and the solution is maintained at, say, C.

The temperaturecan be varied were wide ranse but: best results are obtained at temperatures between 0 and 50 C.

' When theabsorption of oxygen is substantially complete, thesolution is evaporated in vacuo to about 200 ml. The sirup' is then mixed with 2 liters of ethyl alcohol. The clear alcoholic solution, which contains the excess, potassium hy- -droxide,is decanted from the mill! residue which contains potassium trihydroxyglutarate.

The sirupy residue is seeded with potassium ,d-arabo-trihydroxyglutarate and the crystals which form on standing are separated by filtration. The potassium d-arabo-trihydroxyglutarate may be used as such or itmay be converted to d-arabo-trihydroxyglutaric acid in the usual manner. p I

, Should glucuronic acid be used as 'a starting material.instead of galacturonic acid, the. same; procedure is followed, and the resultingproduct v r is the same, namely, potassium d-arabof-t'rihydroxyglutarate. J p v. 1 p

' mExampleZ A 10% solution 0!. crude potassium 'galac'turohate may first be prepared, say, by neutralizing the liquor from pectic acid .after hydroiysis with pectina's'e' (Rohm and ,Haas Pectinol-loo). The

solution-oi potassium galacturonate is cooled to approximately 0 C. It is then saturated with oxygen and suiiicient 'potassium'hydroxideis" added to give 1 mole per liter. The solution is shaken with'oxygen until it is no longer absorbed.-

, The resulting salt of trihydroxyglutaric acid is then converted to an insoluble basic calcium salt by the addition-oi calcium chloride. The basic calcium saltmay be collected on a filter and washed with water. ,It maybethen'convertedtoj triliydroxyglutaric acid by the addition 01- sumv -cient sulphuric acid to remove the calcium as v,

calcium sulphate.

Example 3 When using the sodium calcium galacturonate described in my copending application Serial No.

450,065, filed July 7, 1942, the procedure is conveniently as follows: approximately 100 gramsoi sodium calcium galacturonate is suspended in one liter of normal sodium hydroxide solution con-v I taining 15 grams of sodium carbonate. Oxygen is introduced into the mixture which is maintained in a state of agitation at a convenient temperature, say, 25 C. When the absorption of oxygen ceases,the operation is interrupted, and

the mixture which contains trihydroxygiutarate is filtered.

The sodium trihydroxyglutarate may becrystallized from the filtered solution, or it maybe converted to the insoluble basic calcium salt by the adddition of calcium chloride as set torthin Example 2.

In the event that tree trihydroxygiutaric acid is desired, it may be separated from the filtered solution which contains sodium trihydr'oxyglutarate by acidification with a-mineral acid,.

' such as sulphuric acid; The solutionis then evaporated to remove the volatile acids, and the residue extracted with alcohol. The tree trihy-- 'droxyglutaric acid crystallizes from the alcoholic solution. I

In each of the foregoing examples, upon the mixing oi. the uronic; acid or'itssalt and the alkali. oxygen is preferably supplied in excess oi the requirements of the reaction and maintained in intimate contact with the reaction mixture. This may be accomplished conveniently by vigorous stirring of the mixture while supplying the oxygen under pressure. when air is used as the source 01' oxygen, it is preferable to conduct the oxidation reaction under a pressure of, say, two or three atmospheres.

The invention may be variously modified and embodied within the scope of the subjoined claims.

Iclaim:

1. A step in the process of forming polyhydroxydicarboxylic acid, which comprises the oxidation of a uronic acid in alkaline solution with oxygen.

2. The process which comprises the oxidation 01' a uronic acid in alkaline solution with air, said mixture being under pressure during said oxidation, and the separation of the salt of trihydroxyglutaric acid.

3. The process which comprises the oxidation of galacturonlc acid in alkaline solution with oxygen, and the separation of d-arabo-trihydroxyslutarate.

4. The process which comprises the oxidation of an alkaline metal galaturonate with oxygen and the separation oi the resulting alkaline metal trihydroxyglutarate.

5. The process which comprises subjecting to oxygen an alkaline solution of a galacturonate,

and separating the resulting trihydroxyglutarate. 6. The process which comprises the oxidation of potassium galacturonate with oxy en, and

separating the resulting potassium tridydroxyi glutarate.

7. The process which comprises the oxidation of an alkaline metal galacturonate with oxygen and separating the resulting trihydroxyglutarate.

8. The process which comprises the mixing of sodium calcium galacturonate with aqueous sodium hydroxide containing sodium carbonate, then treating with oxygen, and separating the resulting trihydroxyglutarate.

9. The process of forming trihydroxyglutaric acid, which comprises the oxidation of sodium calcium galacturonate in alkaline solution with oxygen, acidification of the reaction mixture and separating the resulting trihydroxyglutaric acid.

10. The process which comprises the oxidation oi sodium galacturonate with oxygen in the presence of approximately normal alkali and the a separation of the resulting sodium trihydroxyglutarate.

11. The process oi. forming trihydroxyglutaric acid which comprises the oxidation 01' sodium calcium galacturonate in alkaline solution with oxygen, separating the resulting trihydroxyglutarate in the form of a calcium salt, and converting said calcium salt to trihydroxyglutaric acid by acidification.

HORACE S. ISBELL. 

